Biology Lecture Test #3 - Life on earth is protected from...

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Life on earth is protected from ultraviolet or UV radiation by a layer of ozone molecules (03) that is present in the stratosphere between 6 to 30 miles above earth’s surface. UV radiation is highly energetic. Ultraviolet light striking ozone and oxygen causes reactions that break down as well as regenerate ozone . In the process, UV radiation is converted to heat, and the overall level of ozone remains reasonably constant. Some scientists believe that the ozone layer is disappearing due to the accumulation of chlorofluorocarbons (CFC’s). These were chemicals used in refrigeration and aerosol cans. Supposedly, these chemicals rose to the stratosphere and the chlorine in them combined with 03 reducing it to 02. Scientists say that the effect is most apparent over Antarctica, where cold winter temperatures facilitate these atmospheric reactions. Scientists have documented that it is a seasonal phenomenon that grows and shrinks in an annual cycle. CH. 31 Homeostasis and the Organization of the Animal Body Homeostasis - stable internal environment. There may be some changes, but they fluctuate within a range. The equilibrium conditions are maintained by mechanisms known as feedback systems. Negative feedback- a change in a variable being monitored triggers a control mechanism to counteract further change in the same direction. There is a reverse in the initial change. Positive feedback - a change in some variable that triggers mechanisms that amplify rather than reverse the change. The systems of the healthy human body work together. Numerous mechanisms are constantly at work helping to maintain homeostasis. They respond to various stimuli that change as the animal’s activities and environment changes.
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Cells>Tissues>Organs>Organ Systems Similar cells are incorporated into tissues. Tissues are groups of cells with a common structure and function. *Tissues are the building blocks of organs. Ex. Stomach, small intestine, kidneys, urinary bladder. *Tissues perform specific functions. Organs are organized into organ systems. Ex. Digestive system There are four major categories of animal tissues: epithelial tissue, connective tissue, muscle tissue, or nerve tissue. These are present in all but the simplest animals. Epithelial cells form epithelial tissues. Epithelial tissues are bound to connective tissue and form continuous sheets of cells called membranes. These membranes cover the body and line body cavities such as the mouth, stomach, bladder. The free surface of the epithelium is exposed to air or fluid. Membranes create barriers that prevent most substances from crossing. Epithelial cells are packed closely together and connected to one another. Epithelial tissues are continuously lost and replaced by mitotic cell divisions. The stomach lining is completely replaced every 2 to 3 days. Your skin’s outer membrane is the epidermis and is replaced about twice a month.
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This note was uploaded on 06/11/2008 for the course BIOL 11031 taught by Professor Brickman during the Spring '08 term at University of Georgia Athens.

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Biology Lecture Test #3 - Life on earth is protected from...

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